1. Field of the Invention
The present invention relates to a thin film magnetic device having a thin film coil and a magnetic film and a method of manufacturing the same.
2. Description of the Related Art
Hitherto, in the field of electronic devices for various uses, a thin film magnetic device such as a thin film inductor or a thin film transducer including a thin film coil and a magnetic film is widely used as an integrated passive component.
FIGS. 27A and 27B show an example of a conventional thin film magnetic device (thin film inductor 101) constructed by a rectangular spiral coil. FIG. 27A shows a configuration in plan view, and FIG. 27B shows a configuration in cross section taken along line III-III of FIG. 27A. The thin film inductor 101 has a stack structure including, in order in the Z axis direction, an insulating film 112, a rectangular spiral coil 113 having terminals 113T1 and 113T2, and a magnetic film 114 having an opening 115 in its center portion over a substrate 111. In the magnetic film 114, by application of a predetermined magnetic field in the X axis direction at the time of film formation or the like, a magnetization easy axis Me is formed in the magnetic field application direction (X axis direction), and a magnetization hard axis Mh is formed in a direction (Y axis direction) orthogonal to the magnetization easy axis Me, thereby displaying uniaxial anisotropy.
In recent years, high frequency applications in the GHz (gigahertz) band and the like of such a thin film magnetic device are expected. A magnetic film having excellent high frequency characteristics, concretely, a magnetic film having high magnetic permeability in a high frequency area is in demand.
For example, in a conventional thin film magnetic device as shown in FIGS. 27A and 27B, the thin film coil is a rectangular spiral coil. Consequently, coil parts extending in the X axis direction and the Y axis direction exist, and both of the coil parts extending along the magnetization easy axis Me and the magnetization hard axis Mh exist. Therefore, the magnetic permeability of the coil part (in the X axis direction) whose magnetization direction generated by the coil is orthogonal to the magnetization easy axis Me is originally low in a low frequency area but can be maintained to certain extent in a high frequency area. On the other hand, the magnetic permeability of the coil part (in the Y axis direction) whose magnetization direction is parallel with the magnetization easy axis Me is high in the low frequency area but it drops abruptly in the high frequency area. Therefore, the efficiency of use of the magnetic characteristics of the magnetic film is low (in the case of a square spiral coil, about 50%), and it is difficult to achieve high magnetic permeability in the high frequency area.
A technique of improving the magnetic permeability in the high frequency area by forming a plurality of slits in a magnetic film is proposed in, for example, Japanese Unexamined Patent Application Publication (JP-A) Nos. H8-172015 and 2001-143929.
Concretely, JP-A No. H8-172015 discloses a technique such that the magnetization easy axis direction of a magnetic film is varied by using magnetic shape anisotropy of the magnetic film in correspondence with coil parts in two direction of a rectangular spiral coil. More concretely, a magnetic film is separately formed in a magnetic field in correspondence with the coil parts in two directions so that both of the coil parts in two directions become orthogonal to the magnetization easy axis, thereby improving magnetic permeability in the high frequency area.
JP-A No. 2001-143929 discloses a technique such that the magnetization easy axis direction of the magnetic film is rotated by forming fine slits circulating in correspondence with coil parts of a rectangular spiral coil. In a manner similar to the above-described technique, by making both of the coil parts in two directions orthogonal to the magnetization easy axis, the magnetic permeability in the high frequency area is improved.